Wallboard has been used for many years for interior walls of buildings. It is generally manufactured in sheets about 4 feet by 8 feet in size which are nailed to studs or the like to create a wall or a ceiling. Spaces between the sheets, spaces at the corners of walls, and spaces between the ceiling and the walls are usually covered with specially designed tape, and the tape, portions of the wallboard sheets which are adjacent to the tape, and nail holes, if any, are covered or filled with uncured plaster or the like. When the plaster sets, it is sanded to create a smooth surface so that when the walls and ceiling are painted, the tape and nail holes will not be seen.
Professional contractors and others often apply plaster to corners with dispensing apparatus which is designed for that purpose, such as that shown in FIG. 7 of U.S. Pat. No. 2,889,699. That apparatus includes two opposing generally triangular side walls having two straight edges and an arcuate edge which joins the divergent ends of the straight edges. A rectangular wall is secured to the side walls along a straight edge, and an arcuate trailing wall is secured between the arcuate edges of the side walls. A wiping member is anchored near the converging ends of the straight edges and extends between the side walls to the trailing wall. The side walls, rectangular wall, arcuate wall and wiping member form an enclosure for containing uncured plaster. The wiping member may be pivoted towards and away from the rectangular wall to change the volume of the space inside of the enclosure.
In FIG. 7 of U.S. Pat. No. 2,889,699, a spout is located over a substantially round orifice in a portion of the rectangular wall which is away from the converging ends of the side walls. The area of the orifice appears to be about 20 percent of the area of the entire rectangular wall. The spout has a generally conical shape, with the broad end, or base, secured around the orifice. The outlet, or nozzle, is in the narrow end of the spout. When the wiping member is pulled away from the spout, the enclosure may be filled with plaster through a filler hole in the rectangular wall. The wiping member may then be pressed towards the rectangular wall under a predetermined amount of pressure, forcing the plaster through the orifice and spout at a desired rate.
In operation, the dispensing apparatus of FIG. 7 of U.S. Pat. No. 2,889,699 is used in conjunction with a corner head to apply plaster or the like in corners. Since the area of the orifice in the dispensing apparatus is considerably smaller than the area of the rectangular wall, and the transition from the rectangular wall to the spout is abrupt, the plaster does not flow steadily and efficiently within the enclosure and through the orifice and spout. As a result, eddy currents are developed which disturb the flow of the plaster, resulting in the creation of a "dead space" where the plaster hardly moves at all, as will be described in connection with FIG. 4 of this specification.
As a result of the eddy currents and dead space, the plaster comes out of the nozzle in ripples, instead of having a steady flow. Consequently, the dispensed plaster has a wavy, uneven surface, which is undesirable. Also, substantial pressure is required to force the plaster out of the spout, due to the configuration of the apparatus and the presence of the eddy currents and dead space. Applying such pressure is tiring, especially for professional contractors and others who use the apparatus for several hours at a time.
The resulting uneven surface of the plaster, and the substantial pressure required to apply the plaster, also increases the level of skill and attention required to accurately and properly dispense the plaster. At heights over a few feet, a handle is usually secured to the wiping member, so that a ladder or scaffolding is not needed to reach the heights. The use of such a handle requires an even higher level of skill and attention, and proper application of the plaster is made even more difficult because of the substantial pressure which must be applied. Thus, there is a need for apparatus for dispensing plaster and the like in corners which releases the plaster in a steady flow so that the plaster forms a smooth surface, and requires reduced pressure during operation.
The spouts on known plaster dispensers for corners extend generally perpendicular to the rectangular wall, so that part of the base of the spout and part of the rectangular wall extend above the nozzle when the nozzle is directed into a corner. The extension above the nozzle makes it difficult for the user to accurately and properly dispene plaster in corners near the ceiling. Thus, there is a need for apparatus for dispensing plaster in corners which can easily reach corners near the ceiling, and can accurately and properly dispense plaster in such corners.
Accordingly, one object of this invention is to provide new and improved plaster dispensing apparatus for wallboard structures.
Another object is to provide new and improved apparatus for dispensing plaster in corners which releases plaster in a steady flow so that the dispensed plaster has a smooth surface.
Yet another object is to provide new and improved apparatus for dispensing plaster in corners which offers a reduced degree of resistance to the flow of plaster out of the dispensing apparatus.
Still another object is to provide new and improved plaster dispensing apparatus which can easily and accurately dispense plaster in corners near the ceiling.